The present invention relates to a laser diode module for use in optical communications and a method for fabricating the same.
Conventionally, laser diode modules have been used in optical communications, in which a laser diode element (a semiconductor laser element) and an optical fiber for allowing the light from the laser diode element to propagate therethrough are optically coupled in a module. An example of such laser diode modules is disclosed in the European Patent Application EP 0 717297 A2. One that is disclosed therein is a laser diode module shown in FIG. 3. For example, as shown in FIG. 3(c), the laser diode module has a metallic base 1 and a laser diode element 3 that is fixedly disposed on a element mount block 2 secured to the upper side of the base 1.
A lens formed fiber 8 is provided as opposed to the laser diode element 3. The lens formed fiber 8 has a lens (not shown in the figure) formed on the distal end of the optical fiber for receiving laser beams from the laser diode element 3. The lens formed fiber 8 is secured to the ferrule 4 with the distal end thereof, on which the lens is provided, protruded through the distal end of a ferrule 4 toward the laser diode element 3.
Moreover, with the lens formed fiber 8 and the laser diode element 3 aligned with each other, the front side edge portions of the ferrule 4 near the laser diode element 3 are fixedly sandwiched on the both sides thereof by means of a ferrule front fixing part 15. On the other hand, the rear side edge portions of the ferrule 4 furthest from the laser diode element 3 are fixed to the base 1 via a rear fixing part 16. Furthermore, the ferrule 4 is formed in a cylindrical shape or in a shape having a U-shaped groove (in FIG. 3, a cylindrically shaped one is shown).
The aforementioned ferrule front fixing part 15 is disposed, with the part 15 guided by means of a guide portion 11, spaced approximately 0 to 5 xcexcm to a side surface of the ferrule 4 at both sides (on the sides of both side portions) of the ferrule 4 and is fixed to the guide portion 11. After the part 15 has been fixed to the guide portion 11, the ferrule 4 is fixedly YAG-welded to the ferrule front fixing part 15, thus a sandwiched portion 9 is formed.
Furthermore, in such a laser diode module, the lens formed at the distal end of the lens formed fiber 8 is machined to obtain a high optical coupling efficiency with the laser diode element 3. However, the tolerance for optical fiber dislocation in optical coupling is extremely small. For this reason, it is inevitably necessary to fixedly align the aforementioned lens formed fiber 8 with the laser diode element 3 with an extremely high accuracy. This requires much higher accuracy compared with a case where one or more minute optical lenses such as spherical and aspherical lenses are disposed in between the edge surface of an ordinary optical fiber with no lens attached thereto and the laser diode element 3 to align the laser diode element 3 with the lens and the optical fiber.
When the aforementioned laser diode module is fabricated, the lens formed fiber 8 is aligned to obtain maximum coupling efficiency with laser diode 3. Thereafter, as shown in FIG. 3(a), the ferrule front fixing part 15 is disposed at the both sides (at the surfaces of the both sides) of the front side (the side near the laser diode element 3) of the ferrule 4 in between the ferrule 4 and the guide portion 11, which are provided with a spacing therebetween. Furthermore, the guide portion 11 is fixedly provided on the base 1 or formed in one piece with the base 1. Then, the ferrule front fixing part 15 is adapted to be guided by means of the guide portion 11 so as to be able to slide on the surface of the base 1 in the direction (toward X direction in the figure) substantially orthogonal to the beam axis of the ferrule 4. Here, the spacing between the ferrule front fixing part 15 and a side surface of the ferrule 4 is adjusted to within the range of approximately 0 to 5 xcexcn.
Thereafter, as shown in FIG. 3(b), after the ferrule front fixing part 15 is fixedly welded to the guide portion 11 at a plurality of welded portions 7, the ferrule front fixing part 15 and the ferrule 4 are fixedly YAG-welded. The lens formed fiber 8 is dislocated to the laser diode 3 by this YAG-welding. This fixed position is the sandwiched portion 9 of the ferrule 4. After that, for example as shown in FIG. 4, the edge of the rear side of the ferrule 4 (the side furthest from the laser diode element 3) is moved for alignment by a fulcrum at the sandwiched portion 9. Thus, the laser diode element 3 and the lens formed fiber 8 are re-aligned. Furthermore, in FIG. 4, reference number 5 shows a lens provided on the fiber.
Then, under the state of the aforementioned re-alignment, the rear fixing part 16 is disposed on the edge portion of the rear side of the ferrule 4 as shown in FIG. 3(c). After the rear fixing part 16 has been secured to the base 1, the ferrule 4 is fixedly YAG-welded to the rear fixing part 16. Then, finally, the rear fixing part 16 is permanently deformed by a fulcrum at the sandwiched portion 9 in order to correct a dislocation occurring when the ferrule 4 is fixed to the rear fixing part 16. Thus, final alignment is thereby carried out and the plastic deformation of the rear fixing part 16 allows for sustaining the ferrule 4 in a state of re-alignment.
Furthermore, in the aforementioned laser diode module, the ferrule 4 is fixedly YAG-welded at the front side edge portion of the ferrule 4 after the alignment of the laser diode element 3 with the lens formed fiber 8. However, a certain degree of dislocation will occur upon fixing the ferrule 4 at any cost. Accordingly, in the laser diode module shown in FIG. 3, when the front side edge portion of the ferrule 4 is fixed according to the aforementioned method, this dislocation is reduced as follows. That is, the spacing between a side portion of the ferrule 4 and the ferrule front fixing part 15 is adjusted to within a range of approximately 0 to 5 xcexcm, and thereafter the side portion of the ferrule 4 and the ferrule front fixing part 15 are fixedly welded to each other. This will reduce the displacement of the ferrule at the time of YAG welding between the ferrule front fixing part 15 and the ferrule 4, thus reducing a dislocation when the front side edge portion of the ferrule 4 is fixed.
Subsequently, the lens formed fiber 8 is re-aligned with the laser diode element 3. The reduction in dislocation is also intended to reduce re-alignment displacement of the rear side edge portion of the ferrule 4 by a fulcrum at the fixed portion (the sandwiched portion 9) at this time.
However, in the aforementioned laser diode module, the ferrule 4 is fixedly welded at a re-aligned position using the aforementioned rear fixing part 16 that is fixedly welded to the base 1. This makes it impossible to accurately secure the ferrule 4 at said re-alignment position since, for example, the position of the rear fixing part 16 to which the ferrule 4 is to be fixed becomes misaligned when the rear fixing part 16 is fixedly welded to the base 1. Accordingly, in the fabricating method of laser diode modules, it was necessary to perform final alignment of correcting a dislocation between the re-alignment position and the fixing position of the ferrule 4 with plastic deformation of the rear fixing part 16.
Furthermore, the rear fixing part 16 had to take a complicated shape as shown in FIG. 3(c) with additional cost in order to facilitate the final alignment between the laser diode element 3 and the lens formed fiber 8 by means of the plastic deformation. Consequently, this presented such a problem in that the laser diode module comprising such rear fixing part 16 was provided with an increase in cost.
Furthermore, the deformation of the rear fixing part 16 involved in the final alignment needs to be carried out in expectation of recovery from the deformation due to elastic deformation until the rear fixing part 16 reaches plastic deformation. This presented also another problem in that the final alignment was time consuming and thus the laser diode module was not easily fabricated.
Still furthermore, the displacement of the rear fixing part 16 required upon final alignment relates to distance a from the distal end of a lens 5 to the sandwiched portion 9 that serves as a fulcrum upon re-alignment and distance b from the sandwiched portion 9 to the rear fixing part 16. For example, if a: b is equal to 1:10, then the displacement of the rear side edge portion of the ferrule is ten times as much as a minute displacement of the distal end of the lens 5 and thus the rear fixing part 16 must be deformed by that amount. In addition, as mentioned above, an additional deformation is required to compensate the recovery resulting from elastic deformation. This causes the amount of deformation of the rear fixing part 16 to become naturally larger. Consequently, a strain is prone to develop at the sandwiched portion 9 due to twisting stress, and cracks become prone to develop at the welded portion of the sandwiched portion 9 after some time of use of the laser diode module. This presented such a problem in that the crack caused the characteristics of the laser diode module to deteriorate, reducing the reliability thereof.
The present invention was developed to solve the aforementioned prior art themes. Its object is to provide a laser diode module and a fabricating method therefor that facilitates fabrication to allow for fabricating the same in a short time at a low cost, providing high reliability.
In order to achieve the aforementioned object, the present invention has the following characteristic configurations. A first configuration of the laser diode module of the present invention is characterized in that a laser diode element is fixedly disposed on a fixing portion on a base; with a lens, formed at a distal end of a lens formed fiber, disposed opposite to said laser diode element, the lens formed fiber is fixedly disposed on a ferrule; the distal end side of the lens formed fiber where said lens is formed protrudes through the distal end of the ferrule; with said lens formed fiber and said laser diode element aligned with each other, the front side edge portion of the ferrule on the side near said laser diode element and the rear side edge portion of the ferrule on the side furthest from said laser diode element are fixedly sandwiched on the both sides by means of a fixing part, respectively; the fixing part for fixing said rear side edge portion of the ferrule comprises a pair of ferrule fixing parts; the pair of ferrule fixing parts are secured to the base directly or indirectly with the ferrule fixing parts sandwiching the ferrule on the both sides thereof; and said ferrule fixing parts and the ferrule are fixedly YAG-welded.
Furthermore, a second configuration of the laser diode module of the present invention is characterized in that, in said laser diode module comprising the first configuration, a guide portion is fixed on the base of the rear side edge portion of the ferrule, with a spacing provided on the both sides of the ferrule against said ferrule; and the pair of ferrule fixing parts guided by each guide portion are disposed on the both sides of the ferrule and fixed to said guide portion.
Furthermore, a third configuration of the laser diode module of the present invention is characterized in that, in said laser diode module comprising the first or the second configuration, the pair of ferrule fixing parts for fixing the rear side edge portion of the ferrule are disposed with a spacing within a range of approximately 0 to 5 xcexcm against a side surface of the ferrule; and the ferrule and the ferrule fixing parts are fixedly YAG-welded at a position where the spacing within a range of approximately 0 to 5 xcexcm is sustained.
Still furthermore, a fourth configuration of the laser diode module of the present invention is characterized in that, in said laser diode module comprising the third configuration, a sandwiched portion of the fixing part for fixedly sandwiching the front side edge portion of the ferrule is disposed with a spacing within a range of approximately 0 to 20 xcexcm against a side surface of the ferrule; and the ferrule and the sandwiching portion of the fixing part are fixedly YAG-welded at a position where the spacing within a range of approximately 0 to 20 xcexcm is sustained.
Still furthermore, the method for fabricating the laser diode module of the present invention is a method for fabricating a laser diode module having any one of the first through the fourth configurations of the laser diode module of the present invention, comprising the steps of: at a position where a laser diode element and a lens formed fiber are aligned with each other, by sandwiching the both sides of the front side edge portion of the ferrule on the side near said laser diode element with the sandwiching portion of the ferrule supporting part, fixing said sandwiching portion and said ferrule, and fixing said ferrule fixing parts and the base; thereafter, re-aligning said lens formed fiber by a said laser diode element by displacing for alignment the rear side edge portion of the ferrule with fulcrum at the sandwiching portion comprising said ferrule supporting part; on the both sides of the ferrule, disposing the ferrule fixing parts that slidably move along the surface of said base in a direction substantially orthogonal to the beam axis of said ferrule, guided by a guide portion provided with a spacing against said ferrule on the both sides for sandwiching the rear side edge portion of the ferrule; adjusting a spacing between the ferrule fixing parts and a side surface of the ferrule to within a range of approximately 0 to 5 xcexcm; fixedly welding said ferrule fixing parts to said guide portion; and thereafter, fixedly YAG-welding the ferrule fixing parts and the ferrule at a position having said adjusted spacing within a range of approximately 0 to 5 xcexcm, with said lens formed fiber and said laser diode element re-aligned with each other.
In the present invention provided with the aforementioned configurations, the laser diode element and the lens formed fiber are aligned with each other. Thereafter, the front side edge portion of the ferrule (the edge portion on the side near the laser diode element) on the both sides thereof (the sides of the both side portions) is fixedly sandwiched by means of the ferrule supporting parts (fixing parts).
Here, the fixedly sandwiching method is not limited to a particular one. For example, the sandwiched portion of the ferrule and the ferrule supporting part may be fixedly YAG-welded. Alternatively, as shown in FIG. 2, the ferrule and the ferrule supporting part may be fixed by means of a mechanical configuration. In addition, it is possible to select as appropriate which one of a fixations to give high priority to. Namely, after alignment, either the fixation of the ferrule supporting part and the base, or the fixation of the ferrule supporting part and the ferrule can be selected. The sequence of fixation is not limited to a particular one.
According to the present invention, the ferrule supporting part is provided as a fixing part on the front side edge portion (the ferrule edge portion on the side near the laser diode element) of the ferrule. Then, by a fulcrum at the ferrule sandwiched portion by means of the ferrule supporting part, the rear side edge portion (the side of the ferrule edge portion on the side furthest from the laser diode element) of the ferrule is displaced for alignment. Thereby, the lens formed fiber and the laser diode element are re-aligned with each other. On the both sides for sandwiching the ferrule edge portion on a moving side upon re-alignment, for example, the ferrule fixing parts guided by means of the guide portion provided on the base via a spacing against the ferrule are disposed on the both sides of the ferrule. The spacing between the ferrule fixing parts and a ferrule side surface is adjusted to within a range of approximately 0 to 5 xcexcm. The ferrule fixing parts are fixedly welded to the guide portion, and thereafter the ferrule fixing parts and the ferrule are fixedly YAG-welded. Accordingly, this allows for substantially eliminating a displacement of the ferrule upon fixedly YAG-welding, thus enabling accurately fixing the ferrule edge portion displaced for re-alignment to a re-alignment position.
That is, even when the rear side edge portion of the ferrule is displaced for re-alignment by a fulcrum at the sandwiched portion of the ferrule, upon fixing the edge portion of the ferrule at this re-alignment position, the fixing position may dislocate from the re-alignment position. This requires further additional final alignment after the fixation at the re-alignment position. In this respect, the present invention allows the fixation to be carried out without a substantial dislocation of the fixing position at said re-alignment position from the re-alignment position. Accordingly, this eliminates the necessity of said final alignment, thereby allowing for shortening the time required for alignment involved in the fabrication of the laser diode module. This in turn allows for fabricating the laser diode module easily in a short time, thereby reducing the cost by that amount.
Furthermore, according to the present invention, unlike the laser diode module shown in the conventional example, the final alignment is not required after the fixation at the re-alignment position. Therefore, this will not cause the rear side edge portion of the ferrule to be displaced a great deal to result in a strain developed due to twisting stress at the sandwiched portion at the time of the final alignment after the fixation at the re-alignment position. For this reason, this allows for preventing cracks from developing at the welded portion of the sandwiched portion after some time of use of the laser diode module. In addition, this also prevents such a problem in that a crack causes the characteristics of the laser diode module to deteriorate, resulting in lowering the reliability.
Still furthermore, according to the present invention, unlike the laser diode module shown in the conventional example, it is not necessary to provide complicated-shaped and expensive parts, used for carrying out the final alignment by means of plastic deformation, which facilitate alignment between the laser diode element and the lens formed fiber, on the rear side edge portion of the ferrule. For this reason, the laser diode module can be provided at a low cost by that amount.
As mentioned above, this allows for providing a laser diode module and the fabricating method therefor, which allows for fabricating the same easily in a short time at a low cost and high reliability.